Method of estimating voltage of input terminal of inverter and motor control method using the same

ABSTRACT

A method for estimating a voltage of an input terminal of an inverter includes checking three-phase currents flowing from an inverter to a motor. A voltage of an input terminal of the inverter is calculated based on a plurality of design parameters, the three-phase currents, and PWM duties for determining switching operations of a plurality of switching elements of the inverter.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Korean PatentApplication No. 10-2014-0067187 filed in the Korean IntellectualProperty Office on Jun. 2, 2014, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a method of estimating a voltage of aninput terminal of an inverter and a motor control method using the same.

BACKGROUND

A driving motor of vehicles generates driving power using a batterypower. There are various types of motors such as, a motor for driving awater pump, a motor for driving an air blower, etc.

In general, a DC voltage is supplied as a driving voltage to an inverterfor driving the motor. A voltage sensor is provided or a voltage sensingcircuit is formed on a substrate to measure the DC voltage. When thevoltage sensor (or the voltage sensing circuit) becomes defective, theDC voltage cannot be measured, thereby decreasing a motor controlperformance of the inverter.

FIGS. 9( a) and 9(b) are drawings in which a general sensor and avoltage sensor are compared.

As shown in FIGS. 9( a) and 9(b), when the general sensor (e.g., apressure sensor) generates an output voltage range of 0 V to 5 V, onlythe voltage output range of 0.5 V to 4.5 V is used to determinedisconnection or a short-circuit of the pressure sensor. That is, if 0 Vor 5 V is outputted, the pressure sensor is determined to bedisconnected or short-circuited.

However, in the case of the voltage sensor, even if the disconnection orshort-circuit of the voltage sensor occur, the overall output voltagerange of 0 V to 5 V should be used to sense the voltage, thereby failingto detect such faults.

Due to the disconnection or short-circuit of the voltage sensor, even ifthe driving voltage is supplied normally to the input terminal of theinverter, it can be determined that no driving voltage is supplied(i.e., output voltage=0 V) or the driving voltage exceeds the suppliedvoltage (i.e., output voltage=5 V)

That is, even if the driving voltage is supplied normally, output anddynamic characteristics of the motor deteriorate, and an operation ofthe motor should stop.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention, andtherefore, it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY

The present disclosure has been made in an effort to provide a method ofestimating a voltage of an input terminal of an inverter and a method ofcontrolling a motor using the same that are capable of estimating thevoltage of the input terminal of the inverter even without a voltagesensor, determining a fault of the voltage sensor when provided with thevoltage sensor, and controlling the motor even when the voltage sensorbecomes defective.

A method for estimating a voltage of an input terminal of an inverteraccording to an exemplary embodiment of the present invention includeschecking three-phase currents flowing from an inverter to a motor. Avoltage of an input terminal of the inverter is calculated based on aplurality of design parameters, the three-phase currents, and PWM dutiesfor determining switching operations of a plurality of switchingelements of the inverter.

The step of calculating the voltage of the input terminal of theinverter may include calculating estimated three-phase voltages based onthe plurality of design parameters and the three-phase currents. Avoltage V_(dc) _(—) _(Est) of the input terminal of the inverter may becalculated from an equation of V_(dc) _(—) _(Est)=V_(n) _(—)_(Est)×(PWMduty_(n)−0.5), where V_(n) _(—) _(Est) and PWMduty_(n) arevalues corresponding to the same phase, V_(n) _(—) _(Est) is one of theestimated three-phase voltages, and PWMduty_(n) is one of the PWMduties.

The step of calculating the estimated three-phase voltages may includeconverting the three-phase currents into a D-axis current and a Q-axiscurrent that correspond to a fixed coordinate system; converting theD-axis current and the Q-axis current into a d-axis feedback current anda q-axis feedback current that correspond to a synchronous coordinatesystem. A d-axis estimated voltage and a q-axis estimated voltage arecalculated based on the d-axis feedback current and the q-axis feedbackcurrent. The d-axis estimated voltage and the q-axis estimated voltageare converted into a D-axis estimated voltage and a Q-axis estimatedvoltage that correspond to the fixed coordinate system. The D-axisestimated voltage and the Q-axis estimated voltage are converted intoestimated three-phase voltages that correspond to a three-phasecoordinate system.

The d-axis estimated voltage V_(d) _(—) _(Est) and the q-axis estimatedvoltage V_(q) _(—) _(Est) may be respectively calculated from equationsof

$V_{d\_ Est} = {{R_{s}I_{d\_ feedback}} + {L_{d}\frac{}{t}I_{d\_ feedback}} - {\omega_{e}L_{q}I_{q{\_ feedback}}}}$${V_{q{\_ Est}} = {{R_{s}I_{q{\_ feedback}}} + {L_{q}\frac{}{t}I_{q{\_ feedback}}} - {\omega_{e}L_{d}I_{d{\_ feedback}}} + {\omega_{e}\Psi_{f}}}},$

where I_(d) _(—) _(feedback) is a d-axis feedback current, I_(q) _(—)_(feedback) is a q-axis feedback current, R_(s) is a coil resistance ofa motor armature, L_(d) is a d-axis inductance, ω_(e) is an electricalangular velocity, L_(q) is a q-axis inductance, and Ψ_(f) is a magneticflux interlinkage of a motor armature.

Only the ω_(e)Ψ_(f) may be calculated to calculate the q-axis estimatedvoltage when the I_(d) _(—) _(feedback), the I_(q) _(—) _(feedback), theR_(s), the L_(d), the ω_(e), and the L_(q) are smaller than respectivelyset reference values.

The estimated three-phase voltages may be calculated from a relationshipmap of the electrical angular velocity, the three-phase currents, andthe three-phase voltage commands if the estimated three-phase voltagescalculated from the equations of

$V_{d\_ Est} = {{R_{s}I_{d\_ feedback}} + {L_{d}\frac{}{t}I_{d\_ feedback}} - {\omega_{e}L_{q}I_{q{\_ feedback}}}}$$V_{q{\_ Est}} = {{R_{s}I_{q{\_ feedback}}} + {L_{q}\frac{}{t}I_{q{\_ feedback}}} + {\omega_{e}L_{d}I_{d{\_ feedback}}} + {\omega_{e}\Psi_{f}}}$

based on the d-axis estimated voltage and the q-axis estimated voltageare out of a permissible error range of the experimentally measuredthree-phase voltages.

The estimated three-phase voltages V_(a) _(—) _(Est), V_(b) _(—) _(Est),and V_(c) _(—) _(Est) may be calculated from an equation of

$\begin{bmatrix}V_{a{\_ Est}} \\V_{b{\_ Est}} \\V_{c{\_ Est}}\end{bmatrix} = {{\begin{bmatrix}{R_{s} + {\frac{}{t}L_{a}}} & {\frac{}{t}M_{ab}} & {\frac{}{t}M_{ca}} \\{\frac{}{t}M_{ab}} & {R_{s} + {\frac{}{t}L_{b}}} & {\frac{}{t}M_{bc}} \\{\frac{}{t}M_{ca}} & {\frac{}{t}M_{bc}} & {R_{s} + {\frac{}{t}L_{c}}}\end{bmatrix}\begin{bmatrix}I_{a} \\I_{b} \\I_{c}\end{bmatrix}} - {\quad{\begin{bmatrix}{\omega_{e}\Psi_{f}\sin \; \theta} \\{\omega_{e}\Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix},}}}$

where I_(a), I_(b), and I_(c) are three-phase currents, R_(s) is a coilresistance of a motor armature, L_(a,b,c) are magnetic inductances ofrespective phases, M_(ab,bc,ca) are inter-phase mutual inductances,ω_(e) is an electrical angular velocity, Ψ_(f) is a magnetic fluxinterlinkage of a motor armature, and θ is an angle between a d-axis andan a-phase.

Only the

$\quad\begin{bmatrix}{\omega_{e}\Psi_{f}\sin \; \theta} \\{\omega_{e}\Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix}$

may be calculated to calculate the estimated three-phase voltages if theI_(a), I_(b), and I_(c), the R_(s), the L_(a,b,c), the M_(ab,bc,ca), andω_(e) the are smaller than respectively set reference values.

The estimated three-phase voltages may be calculated from a relationshipmap of the electrical angular velocity, the three-phase currents, andthe three-phase voltage commands if the estimated three-phase voltagescalculated from the equation of

$\begin{bmatrix}V_{a{\_ Est}} \\V_{b{\_ Est}} \\V_{c{\_ Est}}\end{bmatrix} = {{\begin{bmatrix}{R_{s} + {\frac{}{t}L_{a}}} & {\frac{}{t}M_{ab}} & {\frac{}{t}M_{ca}} \\{\frac{}{t}M_{ab}} & {R_{s} + {\frac{}{t}L_{b}}} & {\frac{}{t}M_{bc}} \\{\frac{}{t}M_{ca}} & {\frac{}{t}M_{bc}} & {R_{s} + {\frac{}{t}L_{c}}}\end{bmatrix}\begin{bmatrix}I_{a} \\I_{b} \\I_{c}\end{bmatrix}} - {\quad\begin{bmatrix}{\omega_{e}\Psi_{f}\sin \; \theta} \\{\omega_{e}\Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix}}}$

are out of a permissible error range of the experimentally measuredthree-phase voltages.

The calculating the voltage of the input terminal of the inverter mayinclude converting the three-phase currents into a D-axis current and aQ-axis current that correspond to a fixed coordinate system. The D-axiscurrent and the Q-axis current are converted into a d-axis feedbackcurrent and a q-axis feedback current that correspond to a synchronouscoordinate system. A d-axis estimated voltage and a q-axis estimatedvoltage are calculated based on the d-axis feedback current and theq-axis feedback current; converting the PWM duties into a D-axis PWMduty and a Q-axis PWM duty that correspond to the fixed coordinatesystem. The D-axis PWM duty and the Q-axis PWM duty are converted into ad-axis PWM duty and a q-axis PWM duty that correspond to the synchronouscoordinate system. The voltage V_(dc) _(—) _(Est) of the input terminalof the inverter may be calculated from an equation of V_(dc) _(—)_(Est)=V_(m) _(—) _(Est)×(PWMduty_(m)−0.5), where V_(m) _(—) _(Est) andPWMduty_(m) correspond to the same axis, V_(m) _(—) _(Est) is one of thed-axis estimated voltage and the q-axis estimated voltage, andPWMduty_(m) is one of the d-axis PWM duty and the q-axis PWM duty.

A motor control method according to an exemplary embodiment of thepresent invention may include receiving a sensed voltage of an inputterminal of an inverter from a voltage sensor. An estimated voltage ofthe input terminal of the inverter is calculated if the inverter appliesa voltage to a motor. An absolute value between the sensed voltage andthe estimated voltage is compared with a permissible error reference. Anelapsed time after the absolute value exceeds the permissible errorreference is counted if the absolute value is greater than thepermissible error reference. The voltage sensor is determined to be in afault state if the elapsed time is greater than a reference time.

The step of calculating the estimated voltage of the input terminal ofthe inverter may be performed again if the elapsed time is less than orequal to the reference time.

The motor control method may further include resetting the countedelapsed time to zero if the absolute value is less than or equal to thepermissible error reference.

The motor control method may further include comparing the sensedvoltage with a minimum reference voltage and a maximum reference voltageif the voltage sensor is determined to be in the fault state. a wire ofthe voltage sensor is determined to be disconnected or short-circuitedto a ground if the sensed voltage is less than or equal to the minimumreference voltage. The wire of the voltage sensor is determined to beshort-circuited with a power line if the sensed voltage is greater thanor equal to the maximum reference voltage.

The motor control method may further include determining that thevoltage sensor is in a rationality fault state if the voltage sensor isdetermined to be in the fault state and the sensed voltage is greaterthan the minimum reference voltage and less than the maximum referencevoltage.

The motor control method may further include controlling the motor in afail-safe mode using the estimated voltage instead of the sensed voltageif the voltage sensor is determined to be in the fault state.

The motor control method may further include limiting a maximum outputspeed and a maximum output torque of the motor if the voltage sensor isdetermined to be in the fault state.

The calculating the estimated voltage of the input terminal of theinverter may include checking three-phase currents flowing from theinverter to the motor, and the estimated voltage of the input terminalof the inverter may be calculated based on a plurality of designparameters, the three-phase currents, and PWM duties for determiningswitching operations of a plurality of switching elements of theinverter.

The calculating the estimated voltage of the input terminal of theinverter may further include calculating estimated three-phase voltagesbased on the plurality of design parameters and the three-phasecurrents. The estimated voltage V_(dc) _(—) _(Est) of the input terminalof the inverter may be calculated from an equation of V_(dc) _(—)_(Est)=V_(n) _(—) _(Est)×(PWMduty_(n)−0.5), where V_(n) _(—) _(Est) andPWMduty_(n) are values corresponding to the same phase, V_(n) _(—)_(Est) is one of the estimated three-phase voltages, and PWMduty_(n) isone of the PWM duties.

The step of calculating the estimated three-phase voltages may includeconverting the three-phase currents into a D-axis current and a Q-axiscurrent that correspond to a fixed coordinate system. The D-axis currentand the Q-axis current are converted into a d-axis feedback current anda q-axis feedback current that correspond to a synchronous coordinatesystem. A d-axis estimated voltage and a q-axis estimated voltage arecalculated based on the d-axis feedback current and the q-axis feedbackcurrent. The d-axis estimated voltage and the q-axis estimated voltageare converted into a D-axis estimated voltage and a Q-axis estimatedvoltage that correspond to the fixed coordinate system. The D-axisestimated voltage and the Q-axis estimated voltage are converted intoestimated three-phase voltages that correspond to a three-phasecoordinate system. The d-axis estimated voltage V_(d) _(—) _(Est) andthe q-axis estimated voltage V_(q) _(—) _(Est) may be respectivelycalculated from equations of

$V_{d\_ Est} = {{R_{s}I_{d\_ feedback}} + {L_{d}\frac{}{t}I_{d\_ feedback}} - {\omega_{e}L_{q}I_{q{\_ feedback}}}}$${V_{q{\_ Est}} = {{R_{s}I_{q{\_ feedback}}} + {L_{q}\frac{}{t}I_{q{\_ feedback}}} - {\omega_{e}L_{d}I_{d{\_ feedback}}} + {\omega_{e}\Psi_{f}}}},$

where I_(d) _(—) _(feedback) is a d-axis feedback current, I_(q) _(—)_(feedback) is a q-axis feedback current, R_(s) is a coil resistance ofa motor armature, L_(d) is a d-axis inductance, ω_(e) is an electricalangular velocity, L_(q) is a q-axis inductance, and Ψ_(f) is a magneticflux interlinkage of a motor armature.

Only the ω_(e)Ψ_(f) may be calculated to calculate the q-axis voltagecommand if the I_(d) _(—) _(feedback), the I_(q) _(—) _(feedback)) theR_(s), the L_(d), the ω_(e), and the L_(q) are smaller than respectivelyset reference values.

The estimated three-phase voltages may be calculated from a relationshipmap of the electrical angular velocity, the three-phase currents, andthe three-phase voltage commands if the estimated three-phase voltagescalculated from the equations of

$V_{d\_ Est} = {{R_{s}I_{d\_ feedback}} + {L_{d}\frac{}{t}I_{d\_ feedback}} - {\omega_{e}L_{q}I_{q{\_ feedback}}}}$$V_{q{\_ Est}} = {{R_{s}I_{q{\_ feedback}}} + {L_{q}\frac{}{t}I_{q{\_ feedback}}} - {\omega_{e}L_{d}I_{d{\_ feedback}}} + {\omega_{e}\Psi_{f}}}$

based on the d-axis estimated voltage and the q-axis estimated voltageare out of a permissible error range of the experimentally measuredthree-phase voltages.

The estimated three-phase voltages V_(a) _(—) _(Est), V_(b) _(—) _(Est),and V_(c) _(—) _(Est) may be calculated from an equation of

$\quad{\begin{bmatrix}V_{a{\_ Est}} \\V_{b{\_ Est}} \\V_{c{\_ Est}}\end{bmatrix} = {{\begin{bmatrix}{R_{s} + {\frac{}{t}L_{a}}} & {\frac{}{t}M_{ab}} & {\frac{}{t}M_{ca}} \\{\frac{}{t}M_{ab}} & {R_{s} + {\frac{}{t}L_{b}}} & {\frac{}{t}M_{bc}} \\{\frac{}{t}M_{ca}} & {\frac{}{t}M_{bc}} & {R_{s} + {\frac{}{t}L_{c}}}\end{bmatrix}\begin{bmatrix}I_{a} \\I_{b} \\I_{c}\end{bmatrix}} - {\quad{\begin{bmatrix}{\omega_{e}\Psi_{f}\sin \; \theta} \\{\omega_{e}\Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix},}}}}$

where I_(a), I_(b), and I_(c) are three-phase currents, R_(s) is a coilresistance of a motor armature, L_(a,b,c) are magnetic inductances ofrespective phases, M_(ab,bc,ca) are inter-phase mutual inductances,ω_(e) is an electrical angular velocity, Ψ_(f) is a magnetic fluxinterlinkage of a motor armature, and is an angle between a d-axis andan a-phase.

Only the

$\quad\begin{bmatrix}{\omega_{e}\; \Psi_{f}\sin \; \theta} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix}$

may be calculated to calculate the estimated three-phase voltage if theI_(a), I_(b), and I_(c), the R_(s), the L_(a,b,c), the M_(ab,bc,ca), andthe ω_(e) are smaller than respectively set reference values.

The estimated three-phase voltages may be calculated from a relationshipmap of the electrical angular velocity, the three-phase currents, andthe three-phase voltage commands if the estimated three-phase voltagescalculated from the equation of

$\begin{bmatrix}V_{a\_ Est} \\V_{b\_ Est} \\V_{c\_ Est}\end{bmatrix} = {{\begin{bmatrix}{R_{s} + {\frac{}{t}L_{a}}} & {\frac{}{t}M_{ab}} & {\frac{}{t}M_{ca}} \\{\frac{}{t}M_{ab}} & {R_{s} + {\frac{}{t}L_{b}}} & {\frac{}{t}M_{bc}} \\{\frac{}{t}M_{ca}} & {\frac{}{t}M_{bc}} & {R_{s} + {\frac{}{t}L_{c}}}\end{bmatrix}\left\lbrack \begin{matrix}I_{a} \\I_{b} \\I_{c}\end{matrix} \right\rbrack} - {\quad\begin{bmatrix}{\omega_{e}\; \Psi_{f}\sin \; \theta} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix}}}$

are out of a permissible error range of the experimentally measuredthree-phase voltages.

The step of calculating the estimated voltage of the input terminal ofthe inverter may include converting the three-phase currents into aD-axis current and a Q-axis current that correspond to a fixedcoordinate system. The D-axis current and the Q-axis current areconverted into a d-axis feedback current and a q-axis feedback currentthat correspond to a synchronous coordinate system. A d-axis estimatedvoltage and a q-axis estimated voltage are calculated based on thed-axis feedback current and the q-axis feedback current. The PWM dutiesare converted into a D-axis PWM duty and a Q-axis PWM duty thatcorrespond to the fixed coordinate system. The D-axis PWM duty and theQ-axis PWM duty are converted into a d-axis PWM duty and a q-axis PWMduty that correspond to the synchronous coordinate system. The estimatedvoltage V_(dc) _(—) _(Est) of the input terminal of the inverter iscalculated from the equation of V_(dc) _(—) _(Est)=V_(m) _(—)_(Est)×(PWMduty_(m)−0.5), where V_(m) _(—) _(Est) and PWMduty_(m) arevalues that correspond to the same axis, V_(m) _(—) _(Est) is one of thed-axis estimated voltage and the q-axis estimated voltage, andPWMduty_(m) is one of the d-axis PWM duty and the q-axis PWM duty.

As described above, according to the exemplary embodiment of the presentinvention, the voltage of the input terminal of the inverter can beestimated even without a voltage sensor, thereby reducing any additionalcost.

When the voltage sensor is provided to measure the voltage of the inputterminal of the inverter, the voltage of the input terminal of theinverter can be estimated, thereby effectively determining the fault ofthe voltage sensor.

In addition, even if the voltage sensor is faulty, the motor can becontrolled normally, thereby removing a risk involved in the motorcontrol using the wrongly sensed voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a motor control system for torque controlaccording to an exemplary embodiment of the present invention.

FIG. 2 is a block diagram of a motor control system for speed controlaccording to an exemplary embodiment of the present invention.

FIG. 3 is a circuit diagram of an inverter according to an exemplaryembodiment of the present invention.

FIGS. 4A and 4B are block diagrams of the motor control system accordingto the exemplary embodiment of the present invention.

FIGS. 5A and 5B are flowcharts illustrating a method for estimating avoltage of an input terminal of an inverter according to an exemplaryembodiment of the present invention.

FIGS. 6A and 6B are block diagrams of a motor control system accordingto another exemplary embodiment of the present invention.

FIG. 7 is a flowchart of a motor control method according to anotherexemplary embodiment of the present invention.

FIG. 8 is a graph in which an estimated voltage according to theexemplary embodiment of the present invention and a measured voltage arecompared.

FIGS. 9( a) and 9(b) are drawings in which a general sensor and avoltage sensor are compared.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown.

Parts that are irrelevant to the description will be omitted to clearlydescribe the present invention, and the same or similar constituentelements will be designated by the same reference numerals throughoutthe specification.

Further, in the drawings, each element is arbitrarily illustrated forconvenience of description, and the present invention is not necessarilylimited to those illustrated in the drawings.

FIG. 1 is a block diagram of a motor control system for torque controlaccording to an exemplary embodiment of the present invention. FIG. 2 isa schematic block diagram of a motor control system for speed controlaccording to an exemplary embodiment of the present invention.

As shown in FIG. 1, a motor controller 30 for torque control accordingto an exemplary embodiment of the present invention may include acurrent command generator 310, a current controller 320, a coordinatetransformer 330, and a pulse-width modulator (PWM) signal generator 340.That is, when a motor 40 is a driving motor for generating driving powerof a vehicle, the motor controller 30 may include the current commandgenerator 310 to which torque commands are applied.

Alternatively, as shown in FIG. 2, a motor controller 35 for speedcontrol according to the exemplary embodiment of the present inventionmay include a velocity controller 315, a current controller 325, acoordinate transformer 335, and a PWM signal generator 345. That is,when a motor 45 is a driving motor for a water pump or air blower, themotor controller 35 may include the velocity controller 315 to whichvelocity commands are applied.

A description will now be given based on the motor controller 30 fortorque control.

Since the motor controller 35 for speed control is similar to the motorcontroller 30 for controlling the driving motor, except that thevelocity controller 315 for speed control to which the velocity commandsare applied is further included instead of the current command generator310, a detailed description will be omitted.

FIG. 3 is a drawing of a circuit structure of an inverter according tothe according to an exemplary embodiment of the present invention.

As shown in FIG. 3, a driving voltage V_(DC) is applied to an inverter20.

The inverter 20 includes a plurality of switching elements S₁ to S₆, andthe voltage is supplied to three-phase loads Z₁ to Z₃ according toswitching operations of the switching elements S₁ to S₆.

The switching element S₁, the switching element S₄, and the load Z₁ arecoupled to a node N₁. The switching element S₁ and the switching elementS₄ complementarily perform the switching operations. That is, when theswitching element S₁ is in an on-state, the switching element S₄ is inan off-state. When the switching element S₁ is turned on, a DC voltageV_(DC)/2 is supplied to the load Z₁. When the switching element S₄ isturned on, a DC voltage −V_(DC)/2 is supplied to the load Z₁. Accordingto the switching operations of the switching elements S₁ and S₄, an ACvoltage V_(a) is supplied to the load Z₁ and a current I_(a) flowingthrough the load Z₁ is generated.

The switching element S₃, the switching element S₆, and the load Z₂ arecoupled to a node N₂. The switching element S₃ and the switching elementS₆ complementarily perform the switching operations. That is, when theswitching element S₃ is in an on-state, the switching element S₆ is inan off-state. When the switching element S₃ is turned on, the DC voltageV_(DC)/2 is supplied to the load Z₂. When the switching element S₆ isturned on, the DC voltage −V_(DC)/2 is supplied to the load Z₂.According to the switching operations of the switching elements S₃ andS₆, an AC voltage V_(b) of the node N₂ is supplied to the load Z₂, and acurrent I_(b) flowing through the supply is generated.

The switching element S₅, the switching element S₂, and the load Z₃ arecoupled to a node N₃. The switching element S₅ and the switching elementS₂ complementarily perform the switching operations. That is, when theswitching element S₅ is in an on-state, the switching element S₂ is inan off-state. When the switching element S₅ is turned on, the DC voltageV_(DC)/2 is supplied to the load Z₃. When the switching element S₂ isturned on, the DC voltage −V_(DC)/2 is supplied to the load Z₃.According to the switching operations of the switching elements S₅ andS₂, an AC voltage V_(a) of the node N₃ is supplied to the load Z₃ and acurrent I_(c) flowing through the load Z₃ is generated.

The loads Z₁ to Z₃ are coupled to a neutral node. The switchingoperations of the switching elements S₁ to S₆ generate an inter-linevoltage V_(ab) between a line of the load Z₁ and a line of the load Z₂,an inter-line voltage V_(bc) between the line of the load Z₂ and a lineof the load Z₃, and an inter-line voltage V_(ca) between the line of theload Z₃ and the line of the load Z1.

The switching operations of the switching elements S₁, S₃, and S₅ have aphase difference of 120° with respect to each other. A phase differencebetween the switching operations of the switching element S₁ and theswitching element S₃ is 120°, a phase difference between the switchingoperations of the switching element S₃ and the switching element S₅ is120°, and a phase difference between the switching operations of theswitching element S₅ and the switching element S₁ is 120°. Accordingly,a phase difference between the switching operations of the switchingelement S₄ and the switching element S₆ is 120°, a phase differencebetween the switching operations of the switching element S₆ and theswitching element S₂ is 120°, and a phase difference between theswitching operations of the switching element S₂ and the switchingelement S₄ is 120°.

FIGS. 4A and 4B are block diagrams of the motor control system accordingto the exemplary embodiment of the present invention.

As shown in FIG. 4A, a motor control system according to the exemplaryembodiment of the present invention may include a power source 10, aninverter 20, and a motor controller 30.

A driving voltage (DC voltage) is supplied to an input terminal of theinverter 20 from the power source 10, and three-phase currents I_(a),I_(b), and I_(c) are supplied to the motor 40.

The motor controller 30 may be implemented by one or moremicroprocessors that are operated by a predetermined program, and thepredetermined program may include a series of commands for executingrespective steps that are included in a method for controlling theinverter 20 and the motor 40 according to the exemplary embodiment ofthe present invention.

The motor controller 30 may further include a voltage estimator 32 forestimating a voltage of an input terminal of the inverter 20.Alternatively, the voltage estimator 32 may be implemented in adifferent configuration from that of the motor controller 30. Amongprocesses of a method for estimating the voltage of the input terminalof the inverter 20 according to an exemplary embodiment of the presentinvention, which will be described later, some processes may perform bythe motor controller 30 and some other processes may perform by thevoltage estimator 32.

Since the voltage of the input terminal of the inverter 20 can beestimated, it is possible to control the motor 40 even without anadditional voltage sensor for measuring the voltage of the inputterminal of the inverter 20.

As shown in FIG. 4B, the motor controller 30 according to the exemplaryembodiment of the present invention may further include a currentcommand generator 310, a current controller 320, a coordinatetransformer 330, and a PWM signal generator 340.

The current command generator 310 determines a d-axis current commandI_(d) _(—) _(cmd) and a q-axis current command I_(q) _(—) _(cmd)depending on driving conditions of the vehicle. The current commandgenerator 310 has a d-axis current map and a q-axis current map. Whenreceiving a torque command T and a speed w of the motor 40 that arerequired in a current driving condition the vehicle, the current commandgenerator 310 outputs the d-axis current command I_(d) _(—) _(cmd) andthe q-axis current command I_(q) _(—) _(cmd) that correspond to thetorque command T and the speed w.

The current controller 320 includes a d-axis controller 321 and a q-axiscontroller 322. The d-axis controller 321 outputs a d-axis voltagecommand V_(d) _(—) _(cmd) using the d-axis current command I_(d) _(—)_(cmd) received from the current command generator 310 and a d-axisfeedback current I_(d) _(—) _(feedback) received from the coordinatetransformer 330. The q-axis controller 322 outputs a q-axis voltagecommand V_(q) _(—) _(cmd). using the q-axis current command I_(q) _(—)_(cmd) received from the current command generator 310 and a q-axisfeedback current I_(q) _(—) _(feedback) received from the coordinatetransformer 330. The d-axis controller 321 and the q-axis controller 322may be implemented by a proportional integral (PI) controller.

The coordinate transformer 330 converts the d-axis voltage command V_(d)_(—) _(cmd) and the q-axis voltage command V_(q) _(—) _(cmd) that arereceived from the current controller 320 into three-phase voltagecommands V_(a) _(—) _(cmd), V_(b) _(—) _(cmd), and V_(c) _(—) _(cmd).Further, the coordinate transformer 330 converts the three-phasecurrents I_(a), I_(b), and I_(c) flowing from the inverter 20 to themotor 40 into the d-axis feedback current I_(d) _(—) _(feedback) and theq-axis feedback current I_(q) _(—) _(feedback). The three-phase currentsI_(a), I_(b), and I_(c) may be measured by a current sensor 60.Alternatively, the current sensor 60 may measure the two-phase currentsfrom the three-phase currents I_(a), I_(b), and I_(c), and the motorcontroller 30 may measure the remaining one-phase current.

The coordinate transformer 330 includes a synchronous/fixed coordinatetransformer 331, a fixed/three-phase coordinate transformer 332, and athree-phase/fixed coordinate transformer 333, and a fixed/synchronouscoordinate transformer 334. In order to easily design the motorcontroller 30, a three-phase coordinate system [a,b,c] in which ana-phase, a b-phase, and a c-phase are formed at an interval of 120° fromeach other is coordinate-transformed.

A fixed coordinate system [D,Q] is set based on a three-phase coil thatis wound at a stator of the motor 40. A D-axis is a coil direction of ana-phase of the stator, and a Q-axis is a direction that is perpendicularto the coil direction of the a-phase of the stator in terms of anelectrical angle.

A synchronous coordinate system [d,q] is a rotating coordinate systemthat is synchronized with a permanent magnet of a rotor. A d-axis is anN-pole direction of the permanent magnet of the rotor, and a q-axis is adirection that is perpendicular to the N-pole direction of the permanentmagnet of the rotor in terms of the electrical angle.

Based on a position of the rotor of the motor 40 that is received from aposition sensor 50, the synchronous/fixed coordinate transformer 331converts the d-axis voltage command V_(d) _(—) _(cmd) and the q-axisvoltage command V_(q) _(—) _(cmd) into the D-axis voltage command V_(D)_(—) _(cmd) and the Q-axis voltage command V_(Q) _(—) _(cmd) thatcorrespond to the fixed coordinate system [D,Q].

The fixed/three-phase coordinate transformer 332 converts the D-axisvoltage command V_(D) _(—) _(cmd) and the q-axis voltage command V_(Q)_(—) _(cmd) into the three-phase voltage commands V_(a) _(—) _(cmd),V_(b) _(—) _(cmd), and V_(c) _(—) _(cmd) that correspond to thethree-phase coordinate system [a, b, c].

The three-phase/fixed coordinate transformer 333 converts thethree-phase currents I_(a), I_(b), and I_(c) into a D-axis current I_(D)and a Q-axis current I_(Q) that correspond to the fixed coordinatesystem [D,Q].

Based on the position of the rotor of the motor 40 that is received fromthe position sensor 50, the fixed/synchronous coordinate transformer 334converts the D-axis current I_(D) and the Q-axis current I_(Q) into thed-axis feedback current I_(d) _(—) _(feedback) and the q-axis feedbackcurrent I_(q) _(—) _(feedback) that correspond to the synchronouscoordinate system [d,q].

Based on the three-phase voltage commands V_(a) _(—) _(cmd), V_(b) _(—)_(cmd), and V_(c) _(—) _(cmd) that are received from the coordinatetransformer 330, the PWM signal generator 340 determines PWM dutiesPWMduty_(a), PWMduty_(b), and PWMduty_(c).

The PWM duties PWMduty_(a), PWMduty_(b), and PWMduty_(c) may be set tohave values between 0 and 1 (0<PWMduty_(a,b,c)<1). The PWM dutiesPWMduty_(a), PWMduty_(b), and PWMduty_(c) may be set to 0 when a dutyratio (a ratio of a switching cycle to a turned-on time of the switchingelement) is 0% and to 1 when the duty ratio is 100%.

The switching elements S₁ to S₆ of the inverter 20 perform switchingoperations according to the determined PWM duties PWMduty_(a),PWMduty_(b), and PWMduty_(c), and the three-phase currents I_(a), I_(b),and I_(c) flow to the motor 40 from the inverter 20.

FIGS. 5A and 5B are flowcharts illustrating a method for estimating avoltage of an input terminal of an inverter according to an exemplaryembodiment of the present invention.

Referring to FIGS. 5A and 5B, a voltage estimator 32 checks three-phasecurrents I_(c), I_(b), and I_(c) that flow from an inverter 20 to amotor 40 (S10). The two-phase currents among the three-phase currentsI_(c), I_(b), and I_(c) are measured by a current sensor 60, and theremaining one-phase current may be calculated to have a value that makesa sum of the three-phase currents zero.

The voltage estimator 32 checks PWM duties PWMduty_(a), PWMduty_(b), andPWMduty_(c) that determine switching operations of switching elements S₁to S₆ of the inverter 20 (S20). The PWM duties PWMduty_(a), PWMduty_(b),and PWMduty_(c) are determined by a PWM signal generator 340 based onthree-phase voltage commands V_(a) _(—) _(cmd), V_(b) _(—) _(cmd), andV_(c) _(—) _(cmd).

The voltage estimator 32 may calculate a voltage of an input terminal ofthe inverter 20 based on a plurality of design parameters, thethree-phase currents I_(c), I_(b), and I_(c), and the PWM dutiesPWMduty_(a), PWMduty_(b), and PWMduty_(c) (S30).

The voltage estimator 32 may calculate estimated three-phase voltagesV_(a) _(—) _(Est), V_(b) _(—) _(Est), and V_(c) _(—) _(Est) based on theplurality of design parameters and the three-phase currents I_(c),I_(b), and I_(c) (S31).

The voltage estimator 32 may convert the three-phase currents I_(a),I_(b), and I_(c) into a D-axis current I_(D) and a Q-axis current I_(Q)that correspond to a fixed coordinate system [D,Q] (S310), and mayconvert the D-axis current I_(D) and the Q-axis current I_(Q) into ad-axis feedback current I_(d) _(—) _(feedback) and a q-axis feedbackcurrent I_(q) _(—) _(feedback) that correspond to a synchronouscoordinate system [d,q] (S311).

Using Equation 1 below, the voltage estimator 32 may calculate a d-axisestimated voltage V_(d) _(—) _(Est) and a q-axis estimated voltage V_(q)_(—) _(Est) (S312). Equation 1 is a motor voltage equation based on thesynchronous coordinate system.

$\begin{matrix}{{V_{d\_ Est} = {{R_{s}I_{d\_ feedback}} + {L_{d}\frac{}{t}I_{d\_ feedback}} - {\omega_{e}L_{q}I_{q\_ feedback}}}}{{V_{q\_ Est} = {{R_{s}I_{q\_ feedback}} + {L_{q}\frac{}{t}I_{q\_ feedback}} + {\omega_{e}L_{d}I_{d\_ feedback}} + {\omega_{e}\; \Psi_{f}}}},}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

where R_(s) is a coil resistance of a motor armature, L_(d) is a d-axisinductance, ω_(e) is an electrical angular velocity, L_(q) is a q-axisinductance, and Ψ_(f) is a magnetic flux interlinkage of the motorarmature.

The coil resistance of the motor armature R_(s), the d-axis inductanceL_(d), the q-axis inductance L_(q), and the magnetic flux interlinkageof the motor armature Ψ_(f) can be experimentally pre-calculated as thedesign parameters, and the electrical angular velocity ω_(e) can beobtained from the position sensor 50.

The voltage estimator 32 converts the d-axis estimated voltage V_(d)_(—) _(Est) and the q-axis estimated voltage V_(q) _(—) _(Est)calculated by using Equation 1 into the D-axis estimated voltage V_(D)_(—) _(Est) and the Q-axis estimated voltage V_(Q) _(—) _(Est) thatcorrespond to the fixed coordinate system [D,Q] (S313), and may convertthe D-axis estimated voltage V_(D) _(—) _(Est) and the Q-axis estimatedvoltage V_(Q) _(—) _(Est) into estimated three-phase voltages V_(a) _(—)_(Est), V_(b) _(—) _(Est), and V_(c) _(—) _(Est) that correspond to athree-phase coordinate system [a,b,c] (S314).

Based on the estimated three-phase voltages V_(a) _(—) _(Est), V_(b)_(—) _(Est), and V_(c) _(—) _(Est) and the PWM duties PWMduty_(a),PWMduty_(b), and PWMduty_(c), the voltage estimator 32 may calculate thevoltage of the input terminal of the inverter 20 using Equation 2.

V _(dc) _(—) _(Est) =V _(n) _(—) _(Est)×(PWMduty_(n)−0.5),  [Equation 2]

where V_(n) _(—) _(Est) and PWMduty_(n) are values corresponding to thesame phase, V_(n) _(—) _(Est) is one of the estimated three-phasevoltages V_(a) _(—) _(Est), V_(b) _(—) _(Est), and V_(c) _(—) _(Est),and PWMduty_(n) is one of the PWM duties PWMduty_(a), PWMduty_(b), andPWMduty_(c).

Unlike a coordinate-transforming method, the voltage estimator 32 maycalculate the estimated three-phase voltages V_(a) _(—) _(Est), V_(b)_(—) _(Est), and V_(c) _(—) _(Est) using Equation 3. Equation 3 is amotor voltage equation based on the three-phase coordinate system.

$\begin{matrix}{\begin{bmatrix}V_{a\_ Est} \\V_{b\_ Est} \\V_{c\_ Est}\end{bmatrix} = {{\begin{bmatrix}{R_{s} + {\frac{}{t}L_{a}}} & {\frac{}{t}M_{ab}} & {\frac{}{t}M_{ca}} \\{\frac{}{t}M_{ab}} & {R_{s} + {\frac{}{t}L_{b}}} & {\frac{}{t}M_{bc}} \\{\frac{}{t}M_{ca}} & {\frac{}{t}M_{bc}} & {R_{s} + {\frac{}{t}L_{c}}}\end{bmatrix}\left\lbrack \begin{matrix}I_{a} \\I_{b} \\I_{c}\end{matrix} \right\rbrack} - {\quad{\begin{bmatrix}{\omega_{e}\; \Psi_{f}\sin \; \theta} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix},}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

where R_(s) is a coil resistance of a motor armature, L_(a,b,c) aremagnetic inductances of respective phases, M_(ab,bc,ca) are inter-phasemutual inductances, ω_(e) is an electrical angular velocity, Ψ_(f) is amagnetic flux interlinkage of a motor armature, and θ is an anglebetween a d-axis and an a-phase.

The coil resistance of the motor armature R_(s), the magneticinductances of the respective phases L_(a,b,c), the inter-phase mutualinductances M_(ab,bc,ca), and the magnetic flux interlinkage Ψ_(f) ofthe motor armature can be experimentally pre-calculated as the designparameters, and the electrical angular velocity ω_(e) and the angle θbetween the d-axis and the a-phase can be obtained from the positionsensor 50.

Since Equation 3 has more design parameters than Equation 1, it is moreefficient to coordinate-transform the d-axis estimated voltage V_(d)_(—) _(Est) and the q-axis estimated voltage V_(q) _(—) _(Est).

ω_(e)Ψ_(f) of Equation 1 and

$\quad\begin{bmatrix}{\omega_{e}\; \Psi_{f}\sin \; \theta} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix}$

of Equation 3 are counter electromotive force components that aregenerated as the magnetic flux generated from the permanent magnet ofthe rotor passes through a coil of a stator when the motor 40 rotates.When the coil resistance of the motor armature, the inductancecomponents, the currents flowing through the three-phase coil, and theelectrical angular velocity are small, only the counter electromotiveforce components become a determining value. Thus, when the coilresistance of the motor armature R_(s), the inductance components L_(d),L_(q), L_(a,b,c), and M_(ab,bc,ca), the three-phase currents I_(a),I_(b), and I_(c), the d-axis feedback current I_(d) _(—) _(feedback),the q-axis feedback current I_(q) _(—) _(feedback) and the electricalangular velocity ω_(e) are smaller than respectively set referencevalues, the other values are ignored except for the counterelectromotive force components such that only the counter electromotiveforce components are calculated, thereby calculating the q-axisestimated voltage V_(d) _(—) _(Est) and the estimated three-phasevoltages V_(a) _(—) _(Est), V_(b) _(—) _(Est), and V_(c) _(—) _(Est).

The voltage estimator 32 may compare the estimated three-phase voltagesV_(a) _(—) _(Est), V_(b) _(—) _(Est), and V_(c) _(—) _(Est) with theexperimentally measured three-phase voltages (S32). Due to a problemrelated to a design of the motor 40 or non-linearity of the plurality ofdesign parameters, errors may occur between the estimated three-phasevoltages calculated by using Equation 1 or Equation 3 and the measuredthree-phase voltages. When the estimated three-phase voltages are out ofa permissible error range of the measured three-phase voltages, thevoltage estimator 32 may calculate the estimated three-phase voltagesV_(a) _(—) _(Est), V_(b) _(—) _(Est), and V_(c) _(—) _(Est) from arelationship map of the electrical angular velocity, the three-phasecurrents I_(a), I_(b), and I_(c), and the three-phase voltage commandsV_(a) _(—) _(cmd), V_(b) _(—) _(cmd), and V_(c) _(—) _(cmd). The map maybe preset by repeated experiments.

Further, the voltage estimator 32 may calculate the voltage of the inputterminal of the inverter 20 by using Equation 4 based on the d-axisestimated voltage V_(d) _(—) _(Est), the q-axis estimated voltage V_(q)_(—) _(Est), a d-axis PWM duty, and a q-axis PWM duty.

Since the PWM duties PWMduty_(a), PWMduty_(b), and PWMduty_(c) can beseen as vector components, the PWM duties PWMduty_(a), PWMduty_(b), andPWMduty_(c) are coordinate-transformed twice (the three-phase coordinatesystem [a,b,c]=>the fixed coordinate system [D,Q]=>the synchronouscoordinate system [d,q]), thereby calculating the d-axis PWM duty andthe q-axis PWM duty.

V _(dc) _(—) _(Est) =V _(m) _(—) _(Est)(PWMduty_(m)−0.5),  [Equation 4]

where V_(m) _(—) _(Est) and PWMduty_(m) are values corresponding to thesame axis, V_(m) _(—) _(Est) is one of the d-axis estimated voltageV_(d) _(—) _(Est) and the q-axis estimated voltage V_(q) _(—) _(Est),and PWMduty_(m) is one of the d-axis PWM duty and the q-axis PWM duty.

FIG. 8 is a graph in which an estimated voltage according to theexemplary embodiment of the present invention and a measured voltage arecompared.

As shown in FIG. 8, even under a condition where the voltage of theinput terminal of the inverter 20 varies, it can be verified that thecalculated estimated voltages and the measured voltages are within theerror range.

FIGS. 6A and 6B are block diagrams of a motor control system accordingto another exemplary embodiment of the present invention.

Referring to FIGS. 6A and 6B, since a motor control system according tothe current embodiment of the present invention is similar to the motorcontrol system according to the previous exemplary embodiment of thepresent invention, except for an additional voltage sensor 70, adetailed description will be omitted.

The voltage sensor 70 of the motor control system according to thecurrent exemplary embodiment of the present invention may be sufficientif it can measure the voltage of the input terminal of the inverter 20.For example, the voltage sensor 70 may be replaced by a voltage sensingcircuit that is formed on a substrate. Thus, it is to be understood thatthe voltage sensor 70 can include any device that can measure thevoltage of the input terminal of the inverter 20.

Among processes for determining a fault state of the voltage sensor 70according to the exemplary embodiment of the present invention andcontrolling the motor 50 in a fail-safe mode, which will be describedlater, some processes may be performed by the motor controller 30 andsome other processes may be performed by the voltage estimator 32.

FIG. 7 is a flowchart of a motor control method according to anotherexemplary embodiment of the present invention.

Referring to FIG. 7, the voltage estimator 32 receives a sensed voltageU_(dc) _(—) _(sensor) of the input terminal of the inverter 20 from thevoltage sensor 70 (S100).

The voltage estimator 32 determines whether the inverter 20 applies thevoltage to the motor 40 according to the switching operations of theswitching elements S₁ to S₆ (S110).

If the voltage is not applied to the motor 40 from the inverter 20, thevoltage of the input terminal of the inverter 20 cannot be estimatedusing Equation 2.

If the voltage is applied to the motor 40 from the inverter 20, thevoltage estimator 32 calculates an estimated voltage V_(dc) _(—) _(Est)of the input terminal of the inverter 20 (S120). The estimated voltageV_(dc) _(—) _(Est) may be calculated by the method that has beendescribed with reference to FIGS. 5A and 5B.

The voltage estimator 32 compares the sensed voltage V_(dc) _(—)_(Sensor) and the estimated voltage V_(dc) _(—) _(Est) (S130). If themotor 40 is controlled normally, the sensed voltage V_(dc) _(—)_(Sensor) and the estimated voltage V_(dc) _(—) _(Est) should be withinthe error range. The voltage estimator 32 may compare an absolute valuebetween the sensed voltage V_(dc) _(—) _(Sensor) and the estimatedvoltage V_(dc) _(—) _(Est) with the permissible error reference α. Dueto measurement errors of sensors, design errors, etc., there may be adifference between the sensed voltage V_(dc) _(—) _(Sensor) and theestimated voltage V_(dc) _(—) _(Est). The permissible error reference αmay be determined by experiments to have a value that a person ofordinary skill in the art determines.

To compare the sensed voltage V_(dc) _(—) _(Sensor) with the estimatedvoltage V_(dc) _(—) _(Est), the voltage estimator 32 may use variousanalysis techniques (e.g., standard deviation, variance, etc.) insteadof the absolute value and the permissible error reference α.

If the absolute value between the sensed voltage V_(dc) _(—) _(Sensor)and the estimated voltage V_(dc) _(—) _(Est) is greater than thepermissible error reference α, the voltage estimator 32 counts anelapsed time T_(elapsed) after the absolute value exceeds thepermissible error reference α (S140).

The voltage estimator 32 may compare the elapsed time T_(elapsed) and areference time T_(ref) (S150). The reference time T_(ref) may bedetermined by experiments to have a value that a person of ordinaryskill in the art determines.

If the elapsed time T_(elapsed) is greater than the reference timeT_(ref), the voltage estimator 32 may determine that the voltage sensor70 is in a fault state (S160).

The voltage estimator 32 restarts from step S110 if the elapsed timeT_(elapsed) is less than or equal to the reference time T_(ref). In stepS130, if the absolute value between the sensed voltage V_(dc) _(—)_(Sensor) and the estimated voltage V_(dc) _(—) _(Est) is less than orequal to the permissible error reference α, the voltage estimator 32 mayreset the counted elapsed time T_(elapsed) to zero (S170).

If the voltage sensor 70 is determined to be in the fault state, thevoltage estimator 32 compares the sensed voltage V_(dc) _(—) _(Sensor)and a minimum reference voltage V_(low) _(—) _(lim) (5180). The minimumreference voltage V_(low) _(—) _(lim) may be set by a person of ordinaryskill in the art in consideration of the sensed voltage that is detectedin a state where a wire of the voltage sensor 70 is disconnected or isshort-circuited to a ground GND.

If the sensed voltage V_(dc) _(—) _(Sensor) is less than or equal to theminimum reference voltage V_(low) _(—) _(lim), the voltage estimator 32may determine that the wire of the voltage sensor 70 is disconnected orshort-circuited to the ground GND (S190).

If the voltage sensor 70 is determined to be in the fault state, thevoltage estimator 32 compares the sensed voltage V_(dc) _(—) _(Sensor)and a maximum reference voltage V_(high) _(—) _(lim) (S200). The maximumreference voltage V_(high) _(—) _(lim) may be set by a person ofordinary skill in the art in consideration of the sensed voltage that isdetected in a state where the wire of the voltage sensor 70 isshort-circuited with a power line.

If the sensed voltage V_(dc) _(—) _(Sensor) is greater than or equal tothe maximum reference voltage V_(high-lim), the voltage estimator 32 maydetermine that the wire of the voltage sensor 70 is short-circuited withthe power line (S210).

When the voltage sensor 70 is determined to be in the fault state andthe sensed voltage V_(dc) _(—) _(Sensor) is greater than the minimumreference voltage V_(low-lim) and less than the maximum referencevoltage V_(high) _(—) _(lim), the voltage estimator 32 may determinethat the voltage sensor 70 is in a rationality fault state (a fault inwhich the voltage sensor outputs the sensed voltage within the normalrange but actually outputs the wrongly sensed voltage) (S220). When thevoltage sensor 70 is in the rationality fault state, it is difficult toaccurately control the motor 40 using the sensed voltage V_(dc) _(—)_(Sensor).

When the voltage sensor 70 is determined to be in the fault state, thevoltage estimator 32 may control the motor 40 in a fail-safe mode usingthe estimated voltage V_(dc) _(—) _(Est) instead of the sensed voltageV_(dc) _(—) _(Sensor) (S230). In this case, motor control performance atthe same level as that of the case of using the voltage sensor 70 can bemaintained. In addition, for safety, if the voltage sensor 70 isdetermined to be in the fault state, the maximum output speed and torqueof the motor 40 can be limited.

As described above, according to the exemplary embodiment of the presentinvention, the voltage of the input terminal of the inverter 20 can beestimated even without the voltage sensor, thereby reducing anadditional cost.

When the voltage sensor 70 is provided to measure the voltage of theinput terminal of the inverter 20, the voltage of the input terminal ofthe inverter 20 can be estimated, thereby effectively determining thefault of the voltage sensor 70. In addition, even if the voltage sensor70 becomes defective, the motor 40 can be controlled normally, therebyremoving a risk involved in the motor control using the wrongly sensedvoltage.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method for estimating a voltage of an inputterminal of an inverter, comprising steps of: checking three-phasecurrents flowing from an inverter to a motor; and calculating a voltageof an input terminal of the inverter based on a plurality of designparameters, the three-phase currents, and PWM duties for determiningswitching operations of a plurality of switching elements of theinverter.
 2. The method of claim 1, wherein the step of calculating thevoltage of the input terminal of the inverter includes calculatingestimated three-phase voltages based on the plurality of designparameters and the three-phase currents, wherein a voltage V_(dc) _(—)_(Est) of the input terminal of the inverter is calculated from anequation of V_(dc) _(—) _(Est)=V_(n) _(—) _(Est)×(PWMduty_(n)−0.5),where V_(n) _(—) _(Est) and PWMduty_(n) are values corresponding to thesame phase, V_(n) _(—) _(Est) is one of the estimated three-phasevoltages, and PWMduty_(n) is one of the PWM duties.
 3. The method ofclaim 2, wherein the step of calculating the estimated three-phasevoltages includes steps of: converting the three-phase currents into aD-axis current and a Q-axis current that correspond to a fixedcoordinate system; converting the D-axis current and the Q-axis currentinto a d-axis feedback current and a q-axis feedback current thatcorrespond to a synchronous coordinate system; calculating a d-axisestimated voltage and a q-axis estimated voltage based on the d-axisfeedback current and the q-axis feedback current; converting the d-axisestimated voltage and the q-axis estimated voltage into a D-axisestimated voltage and a Q-axis estimated voltage that correspond to thefixed coordinate system; and converting the D-axis estimated voltage andthe Q-axis estimated voltage into estimated three-phase voltages thatcorrespond to a three-phase coordinate system.
 4. The method of claim 3,wherein the d-axis estimated voltage V_(d) _(—) _(Est) and the q-axisestimated voltage V_(q) _(—) _(Est) are calculated from equations of$V_{d\_ Est} = {{R_{s}I_{d\_ feedback}} + {L_{d}\frac{}{t}I_{d\_ feedback}} - {\omega_{e}L_{q}I_{q\_ feedback}}}$${V_{q\_ Est} = {{R_{s}I_{q\_ feedback}} + {L_{q}\frac{}{t}I_{q\_ feedback}} + {\omega_{e}L_{d}I_{d\_ feedback}} + {\omega_{e}\; \Psi_{f}}}},$where I_(d) _(—) _(feedback) is a d-axis feedback current, I_(q) _(—)_(feedback) is a q-axis feedback current, R_(s) is a coil resistance ofa motor armature, L_(d) is a d-axis inductance, ω_(e) is an electricalangular velocity, L_(q) is a q-axis inductance, and Ψ_(f) is a magneticflux interlinkage of the motor armature.
 5. The method of claim 4,wherein only the ω_(e)Ψ_(f) is calculated to calculate the q-axisestimated voltage when the I_(d) _(—) _(feedback), the I_(q) _(—)_(feedback), the R_(s), the L_(d), the ω_(e), and the L_(q) are smallerthan respectively set reference values.
 6. The method of claim 4,wherein the estimated three-phase voltages are calculated from arelationship map of the electrical angular velocity, the three-phasecurrents, and the three-phase voltage commands if the estimatedthree-phase voltages calculated from the equations of$V_{d\_ Est} = {{R_{s}I_{d\_ feedback}} + {L_{d}\frac{}{t}I_{d\_ feedback}} - {\omega_{e}L_{q}I_{q\_ feedback}}}$$V_{q\_ Est} = {{R_{s}I_{q\_ feedback}} + {L_{q}\frac{}{t}I_{q\_ feedback}} + {\omega_{e}L_{d}I_{d\_ feedback}} + {\omega_{e}\; \Psi_{f}}}$ based on the d-axis estimated voltage and the q-axis estimated voltageare out of a permissible error range of the experimentally measuredthree-phase voltages.
 7. The method of claim 2, wherein the estimatedthree-phase voltages V_(a) _(—) _(Est), V_(b) _(—) _(Est), and V_(c)_(—) _(Est) are calculated from an equation of $\begin{bmatrix}V_{a\_ Est} \\V_{b\_ Est} \\V_{c\_ Est}\end{bmatrix} = {{\begin{bmatrix}{R_{s} + {\frac{}{t}L_{a}}} & {\frac{}{t}M_{ab}} & {\frac{}{t}M_{ca}} \\{\frac{}{t}M_{ab}} & {R_{s} + {\frac{}{t}L_{b}}} & {\frac{}{t}M_{bc}} \\{\frac{}{t}M_{ca}} & {\frac{}{t}M_{bc}} & {R_{s} + {\frac{}{t}L_{c}}}\end{bmatrix}\left\lbrack \begin{matrix}I_{a} \\I_{b} \\I_{c}\end{matrix} \right\rbrack} - {\quad{\begin{bmatrix}{\omega_{e}\; \Psi_{f}\sin \; \theta} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix},}}}$ where I_(a), I_(b), and are three-phase currents,R_(s) is a coil resistance of a motor armature, L_(a,b,c) are magneticinductances of respective phases, M_(ab,bc,ca) are inter-phase mutualinductances, ω_(e) is an electrical angular velocity, Ψ_(f) is amagnetic flux interlinkage of the motor armature, θ and is an anglebetween a d-axis and an a-phase.
 8. The method of claim 7, wherein onlythe $\quad\begin{bmatrix}{\omega_{e}\; \Psi_{f}\sin \; \theta} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix}$  is calculated to calculate the estimated three-phasevoltages if the I_(a), I_(b), and I_(c), the R_(s), the L_(a,b,c), theM_(ab,bc,ca) and the ω_(e) are smaller than respectively set referencevalues,
 9. The method of claim 7, wherein the estimated three-phasevoltages are calculated from a relationship map of the electricalangular velocity, the three-phase currents, and the three-phase voltagecommands if the estimated three-phase voltages calculated from theequation of $\begin{bmatrix}V_{a\_ Est} \\V_{b\_ Est} \\V_{c\_ Est}\end{bmatrix} = {{\begin{bmatrix}{R_{s} + {\frac{}{t}L_{a}}} & {\frac{}{t}M_{ab}} & {\frac{}{t}M_{ca}} \\{\frac{}{t}M_{ab}} & {R_{s} + {\frac{}{t}L_{b}}} & {\frac{}{t}M_{bc}} \\{\frac{}{t}M_{ca}} & {\frac{}{t}M_{bc}} & {R_{s} + {\frac{}{t}L_{c}}}\end{bmatrix}\left\lbrack \begin{matrix}I_{a} \\I_{b} \\I_{c}\end{matrix} \right\rbrack} - {\quad\begin{bmatrix}{\omega_{e}\; \Psi_{f}\sin \; \theta} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix}}}$ are out of a permissible error range of theexperimentally measured three-phase voltages.
 10. The method of claim 1,wherein the step of calculating the voltage of the input terminal of theinverter further includes steps of: converting the three-phase currentsinto a D-axis current and a Q-axis current that correspond to a fixedcoordinate system; converting the D-axis current and the Q-axis currentinto a d-axis feedback current and a q-axis feedback current thatcorrespond to a synchronous coordinate system; calculating a d-axisestimated voltage and a q-axis estimated voltage based on the d-axisfeedback current and the q-axis feedback current; converting the PWMduties into a D-axis PWM duty and a Q-axis PWM duty that correspond tothe fixed coordinate system; and converting the D-axis PWM duty and theQ-axis PWM duty into a d-axis PWM duty and a q-axis PWM duty thatcorrespond to the synchronous coordinate system, wherein the voltageV_(dc) _(—) _(Est) of the input terminal of the inverter is calculatedfrom an equation of V_(dc) _(—) _(Est)=V_(m) _(—)_(Est)×(PWMduty_(m)−0.5), where V_(m) _(—) _(Est) and PWMduty_(m)correspond to the same axis, V_(m) _(—) _(Est) is one of the d-axisestimated voltage and the q-axis estimated voltage, and PWMduty_(m) isone of the d-axis PWM duty and the q-axis PWM duty.
 11. A motor controlmethod comprising steps of: receiving a sensed voltage of an inputterminal of an inverter from a voltage sensor; calculating an estimatedvoltage of the input terminal of the inverter if the inverter applies avoltage to a motor; comparing an absolute value between the sensedvoltage and the estimated voltage with a permissible error reference;counting an elapsed time after the absolute value exceeds thepermissible error reference if the absolute value is greater than thepermissible error reference; and determining that the voltage sensor isin a fault state if the elapsed time is greater than a reference time;12. The motor control method of claim 11, wherein the step ofcalculating the estimated voltage of the input terminal of the inverteris performed again if the elapsed time is less than or equal to thereference time.
 13. The motor control method of claim 12, furthercomprising a step of: resetting the counted elapsed time to zero if theabsolute value is less than or equal to the permissible error reference.14. The motor control method of claim 11, further comprising steps of:comparing the sensed voltage with a minimum reference voltage and amaximum reference voltage if the voltage sensor is determined to be inthe fault state; determining that a wire of the voltage sensor isdisconnected or short-circuited to a ground if the sensed voltage isless than or equal to the minimum reference voltage; and determiningthat the wire of the voltage sensor is short-circuited with a power lineif the sensed voltage is greater than or equal to the maximum referencevoltage.
 15. The motor control method of claim 14, further comprising astep of: determining that the voltage sensor is in a rationality faultstate if the voltage sensor is determined to be in the fault state andthe sensed voltage is greater than the minimum reference voltage andless than the maximum reference voltage.
 16. The motor control method ofclaim 11, further comprising a step of: controlling the motor in afail-safe mode using the estimated voltage instead of the sensed voltageif the voltage sensor is determined to be in the fault state.
 17. Themotor control method of claim 16, further comprising a step of: limitinga maximum output speed and a maximum output torque of the motor if thevoltage sensor is determined to be in the fault state.
 18. The motorcontrol method of claim 11, wherein the step of calculating theestimated voltage of the input terminal of the inverter includeschecking three-phase currents flowing from the inverter to the motor,and the estimated voltage of the input terminal of the inverter iscalculated based on a plurality of design parameters, the three-phasecurrents, and PWM duties for determining switching operations of aplurality of switching elements of the inverter.
 19. The motor controlmethod of claim 18, wherein the step of calculating the estimatedvoltage of the input terminal of the inverter further includescalculating estimated three-phase voltages based on the plurality ofdesign parameters and the three-phase currents, wherein the estimatedvoltage V_(dc) _(—) _(Est) of the input terminal of the inverter iscalculated from an equation of V_(dc) _(—) _(Est)=V_(n) _(—)_(Est)×(PWMduty_(n)−0.5), where V_(n) _(—) _(Est) and PWMduty_(n) arevalues corresponding to the same phase, V_(n) _(—) _(Est) is one of theestimated three-phase voltages, and PWMduty_(n) is one of the PWMduties.
 20. The motor control method of claim 19, wherein the step ofcalculating the estimated three-phase voltages includes steps of:converting the three-phase currents into a D-axis current and a Q-axiscurrent that correspond to a fixed coordinate system; converting theD-axis current and the Q-axis current into a d-axis feedback current anda q-axis feedback current that correspond to a synchronous coordinatesystem; calculating a d-axis estimated voltage and a q-axis estimatedvoltage based on the d-axis feedback current and the q-axis feedbackcurrent; converting the d-axis estimated voltage and the q-axisestimated voltage into a D-axis estimated voltage and a Q-axis estimatedvoltage that correspond to the fixed coordinate system; and convertingthe D-axis estimated voltage and the Q-axis estimated voltage intoestimated three-phase voltages that correspond to a three-phasecoordinate system, wherein the d-axis estimated voltage V_(d) _(—)_(Est) and the q-axis estimated voltage V_(q) _(—) _(Est) are calculatedfrom equations of$V_{d\_ Est} = {{R_{s}I_{d\_ feedback}} + {L_{d}\frac{}{t}I_{d\_ feedback}} - {\omega_{e}L_{q}I_{q\_ feedback}}}$${V_{q\_ Est} = {{R_{s}I_{q\_ feedback}} + {L_{q}\frac{}{t}I_{q\_ feedback}} + {\omega_{e}L_{d}I_{d\_ feedback}} + {\omega_{e}\; \Psi_{f}}}},$where I_(d) _(—) _(feedback) is a d-axis feedback current, I_(q) _(—)_(feedback) is a q-axis feedback current, R_(s) is a coil resistance ofa motor armature, L_(d) is a d-axis inductance, ω_(e) is an electricalangular velocity, L_(q) is a q-axis inductance, and Ψ_(f) is a magneticflux interlinkage of the motor armature.
 21. The motor control method ofclaim 20, wherein only the ω_(e)Ψ_(f) is calculated to calculate theq-axis voltage command if the I_(d) _(—) _(feedback), the I_(d) _(—)_(feedback), the R_(s), the L_(d), the ω_(e), and the L_(q) are smallerthan respectively set reference values.
 22. The motor control method ofclaim 20, wherein the estimated three-phase voltages are calculated froma relationship map of the electrical angular velocity, the three-phasecurrents, and the three-phase voltage commands if the estimatedthree-phase voltages calculated from the equation of$V_{d\_ Est} = {{R_{s}I_{d\_ feedback}} + {L_{d}\frac{}{t}I_{d\_ feedback}} - {\omega_{e}L_{q}I_{q\_ feedback}}}$$V_{q\_ Est} = {{R_{s}I_{q\_ feedback}} + {L_{q}\frac{}{t}I_{q\_ feedback}} + {\omega_{e}L_{d}I_{d\_ feedback}} + {\omega_{e}\; \Psi_{f}}}$ based on the d-axis estimated voltage and the q-axis estimated voltageare out of a permissible error range of the experimentally measuredthree-phase voltages.
 23. The motor control method of claim 19, whereinthe estimated three-phase voltages V_(a) _(—) _(Est), V_(b) _(—) _(Est),and V_(c) _(—) _(Est) are calculated from an equation of$\begin{bmatrix}V_{a\_ Est} \\V_{b\_ Est} \\V_{c\_ Est}\end{bmatrix} = {{\begin{bmatrix}{R_{s} + {\frac{}{t}L_{a}}} & {\frac{}{t}M_{ab}} & {\frac{}{t}M_{ca}} \\{\frac{}{t}M_{ab}} & {R_{s} + {\frac{}{t}L_{b}}} & {\frac{}{t}M_{bc}} \\{\frac{}{t}M_{ca}} & {\frac{}{t}M_{bc}} & {R_{s} + {\frac{}{t}L_{c}}}\end{bmatrix}\left\lbrack \begin{matrix}I_{a} \\I_{b} \\I_{c}\end{matrix} \right\rbrack} - {\quad{\begin{bmatrix}{\omega_{e}\; \Psi_{f}\sin \; \theta} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix},}}}$ where I_(a), I_(b), and I_(c) are three-phasecurrents, R_(s) is a coil resistance of a motor armature, L_(a,b,c) aremagnetic inductances of respective phases, M_(ab,bc,ca) are inter-phasemutual inductances, ω_(e) is an electrical angular velocity, Ψ_(f) is amagnetic flux interlinkage of the motor armature, θ and is an anglebetween a d-axis and an a-phase.
 24. The motor control method of claim23, wherein only the $\quad\begin{bmatrix}{\omega_{e}\; \Psi_{f}\sin \; \theta} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix}$  is calculated to calculate the estimated three-phasevoltage if the I_(a), I_(b), and I_(c), the R_(s), the L_(a,b,c), theM_(ab,bc,ca), and the are smaller than respectively set referencevalues.
 25. The motor control method of claim 23, wherein the estimatedthree-phase voltages are calculated from a relationship map of theelectrical angular velocity, the three-phase currents, and thethree-phase voltage commands if the estimated three-phase voltagescalculated from the equation of $\begin{bmatrix}V_{a\_ Est} \\V_{b\_ Est} \\V_{c\_ Est}\end{bmatrix} = {{\begin{bmatrix}{R_{s} + {\frac{}{t}L_{a}}} & {\frac{}{t}M_{ab}} & {\frac{}{t}M_{ca}} \\{\frac{}{t}M_{ab}} & {R_{s} + {\frac{}{t}L_{b}}} & {\frac{}{t}M_{bc}} \\{\frac{}{t}M_{ca}} & {\frac{}{t}M_{bc}} & {R_{s} + {\frac{}{t}L_{c}}}\end{bmatrix}\left\lbrack \begin{matrix}I_{a} \\I_{b} \\I_{c}\end{matrix} \right\rbrack} - {\quad\begin{bmatrix}{\omega_{e}\; \Psi_{f}\sin \; \theta} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta - {\frac{2}{3}\pi}} \right)}} \\{\omega_{e}\; \Psi_{f}{\sin \left( {\theta + {\frac{2}{3}\pi}} \right)}}\end{bmatrix}}}$  are out of a permissible error range of theexperimentally measured three-phase voltages.
 26. The motor controlmethod of claim 18, wherein the step of calculating the estimatedvoltage of the input terminal of the inverter includes steps of:converting the three-phase currents into a D-axis current and a Q-axiscurrent that correspond to a fixed coordinate system; converting theD-axis current and the Q-axis current into a d-axis feedback current anda q-axis feedback current that correspond to a synchronous coordinatesystem; calculating a d-axis estimated voltage and a q-axis estimatedvoltage based on the d-axis feedback current and the q-axis feedbackcurrent; converting the PWM duties into a D-axis PWM duty and a Q-axisPWM duty that correspond to the fixed coordinate system; and convertingthe D-axis PWM duty and the Q-axis PWM duty into a d-axis PWM duty and aq-axis PWM duty that correspond to the synchronous coordinate system,wherein the estimated voltage V_(dc) _(—) _(Est) of the input terminalof the inverter is calculated from the equation of V_(dc) _(—)_(Est)=V_(m) _(—) _(Est)×(PWMduty_(m)−0.5), where V_(m) _(—) _(Est) andPWMduty_(m) are values that correspond to the same axis, V_(m) _(—)_(Est) is one of the d-axis estimated voltage and the q-axis estimatedvoltage, and PWMduty_(m) is one of the d-axis PWM duty and the q-axisPWM duty.
 27. A non-transitory computer-readable recording mediumcomprising computer executable instructions of which cause a motorcontroller to perform the method according to claim 1.